1. Field of the Invention
This invention relates to the oxidation of a liquid, and more particularly, to a method and an apparatus for oxidizing a liquid containing the matter to be oxidized, such as ferrous or sulfurous ions, in the presence or absence of an oxidizing catalyst.
2. Description of the Prior Art
There are a variety of systems which are used for the oxidizing treatment of a liquid containing the matter to be oxidized. They include a system of the type which is used for oxidizing sludge, industrial waste water, a liquid which has absorbed sulfur as a result of the desulfurization of smoke, or the like, and a system of the type which is used for producing a particular treating agent by oxidation.
The former type of system is used for oxidizing, for example, a liquid which has absorbed sulfurous ions as a result of the desulfurization of smoke, or waste water from a factory containing dissolved ferrous ions. It has, however, a number of disadvantages, particularly if the liquid to be treated has a low pH value. The treatment of the liquid requires a long time of reaction by employing a large amount of oxidizing agent in a large apparatus. It sometimes calls for the application of heat. Therefore, it is expensive and yet has a low reaction efficiency.
The latter type of system is used for manufacturing, for example, iron polysulfate which has recently drawn much attention as a coagulant. According to the disclosure of Japanese Patent Application laid open under No. 53195/1974, an acid solution containing ferrous sulfate which occurs as a by-product when waste sulfuric acid is recovered from, for example, the process for pickling iron and steel is oxidized with an oxidizing agent, such as air or oxygen, in the presence of an oxidizing catalyst, such as nitrogen oxide, to produce a basic inorganic high molecular iron polysulfate containing an OH group between ferric sulfate and SO.sub.4.sup.-2. Likewise, Japanese Patent Publication No. 23266/1978 discloses the manufacture of a basic coagulant comprising a double salt formed from iron polychloride and iron sulfate. In either event, however, the liquid to be oxidized has so low a pH value that its oxidation requires a large amount of oxidizing agent, and it has been difficult to manufacture iron polysulfate at a low cost and with a high efficiency.